In reclosable plastic bags or other containers, particularly those containing a zipper type reclosable closure such as taught in U.S. Pat. No. 4,263,079, the container usually carries lips located above the reclosable closure feature, which lips are required to be grasped between the thumb and a finger, for example, and pulled to open the closure. Some degree of force is necessary to open the closure, which is relatively secure to avoid accidental opening. Since such bags are often found in the kitchen, it is not uncommon for one's fingers to be greasy. Since lips of such bags are commonly formed from smooth films such as those formed of polyolefin resin, the ease with which the lips of the bag can be grasped and kept hold of while pulling during opening can be easily negated when the fingers are greasy. Attempts to solve the lip grasping problem have generally included one, two or three large ribs, which are close to the same size as the closure elements themselves, such as illustrated in U.S. Pat. No. 4,363,345, for example. Such large ribs are purported to improve gripping of the container lips by the user during the opening and loading of the container. However, use of large ribs has been found to cause some forming complications because of their size, in that undulations can occur during extrusion. Such large ribs have also been found in many instances not to be as comfortable to the user as they might be, some effort is required on the part of the user to locate the large ribs and such large ribs require considerable amount of resin material to form especially if more than one or two of them are employed.
Other references that teach only slightly roughened opposing surfaces in film containers such as found in U.S. Pat. Nos. 2,197,113 and 3,113,715 are designed primarily to prevent blocking so that the bags are easier to open or to provide a means of venting air from the inside of the container for vacuum packaging, and are not designed to nor effectively provide a gripping function for grasping by fingers.
What the Applicants have found is that a far more desirable, improved arrangement is where the size and the number of protuberance are in between those that are merely employed for roughening a surface as a spacing means for non blocking and those ribs which are large and small in number, such as previously designed to aid in gripping of lips of reclosable plastic bags.